1. Field of the Invention
The present invention relates to a light emitting apparatus and a method for driving the light emitting LED apparatus. The present invention also relates to a display apparatus including the light emitting apparatus.
2. Description of the Related Art
FIG. 20 illustrates a conventional LED driving apparatus. In the conventional LED driving apparatus, a driving current i corresponding to an output establishment value p is applied from a power source 191 to an LED device 192 to drive the LED device 192. The emission intensity of the LED device 192 is controlled by changing the value of the driving current i. In general, the color of light emitted from conventional LED devices does not depend on the value of a driving current. Thus, the emission intensity, of conventional LED devices is changed by control of the driving current value while maintaining the color of light emitted from the LED devices.
The emission intensity of conventional LED devices can be solely changed by control of the driving current value, since the light color of the conventional LED devices is not affected by a change in the driving current value. However, there is another type of LED device having a light color which is altered by a change in the driving current value. When such an LED device is driven by a driving apparatus as shown in FIG. 20, the light color of the LED device is changed along with the emission intensity control thereof. Thus, a desired emission intensity control cannot be conducted.
Conventional AlGaAs semiconductor light emitting devices have a phenomenon In which the wavelength of light emitted therefrom becomes longer as a driving current is Increased (red shift phenomenon). The red shift phenomenon occurs as follows. The light emitting device is heated by supplied power, and the temperature of the device is proportional to the average supplied power. The increased temperature causes the bandgap of the active layer to be reduced, so that the wavelength of light emitted from the device becomes longer (red shift). In other words, the emission intensity and emission wavelength of the light emitting device having the red shift phenomenon are determined by the average power applied to the device. It is not possible to separately control the emission wavelength and emission power of the AlGaAs semiconductor light emitting device using two parameters (peak value and average power) of a driving current pulse.
According to one aspect of the present invention, a light emitting apparatus comprises: a light emitting section for emitting light, a color of the light being blue shifted with a value of a driving current; and a driving section for driving the light emitting section so that the light emitting section emits light having a desired color and a desired intensity, by generating the driving current based on a signal designating the desired color and a signal designating the desired intensity and by applying the driving current to the light emitting section.
In one embodiment of this invention, the driving section comprises: a converting section for converting the color-designating signal to a signal designating a current value in accordance with current versus emission wavelength characteristics of the light emitting section: a calculating section for calculating a signal designating a duty based on the intensity-designating signal and the current value-designating signal, in such a manner that the product of a current value designated by the current value-designating signal and u duty corresponds to the intensity designated by the intensity-designating signal; and e section for generating, as the driving current, a pulse current having the current value and the duty In accordance with the respective current value-designating signal and duty-designating signal.
In one embodiment of this invention, the light emitting section is an LED device.
In one embodiment of this invention, the light emitting section is an LED bullet comprising: an LED device; and a fluorescent excited by light emitted by the LED device to emit light.
In one embodiment of this invention, when the driving current value is changed, a change in an emission wavelength of the LED bullet is larger than a change in an emission wavelength of the LED device.
In one embodiment of this invention, the light emitting apparatus comprises a plurality of the light emitting sections: and a plurality of the driving sections respectively corresponding to the plurality of the light emitting sections. A color and intensity of light emitted by each of the plurality of the light emitting sections is controlled by a corresponding one of the plurality of the driving sections.
In one embodiment of this invention, the color-designating signal is a color signal for designating a color of light to be emitted by the LED device, and the intensity-designating signal is an intensity signal for-designating an intensity of the light to be emitted by the LED device.
In one embodiment of this invention, the color-designating signal is a chromaticity signal for designating a color of light to be emitted by the LED bullet, and the intensity-designating signal is a luminance signal for designating an intensity of the light to be emitted by the LED bullet.
In one embodiment of this Invention, the LED device comprises: an InGaN active layer and an AlGaN layer having two layers, provided on the InGaN active layer. One of the two layers is a first AlGaN layer contacting the InGaN active layer, and the other of the two layers of the AlGaN layer is a second AlGaN layer provided on the first AlGaN layer, the first AlGaN layer is produced at substantially the same growth temperature as the InGaN active layer, and the second AlGaN layer is produced at a growth temperature higher than the growth temperature of the first AlGaN layer.
In one embodiment of this invention, the LED device comprises: an InGaN active layer; and an AlGaN layer having two layers, provided on the InGaN active layer. One of the two layers is a first AlGaN layer contacting the InGaN active layer, and the other of the two layers of the AlGaN layer is a second AlGaN layer provided on the first AlGaN layer, the first AlGaN layer is produced at substantially the same growth temperature as the InGaN active layer, and the second AlGaN layer is produced at a growth temperature higher than the growth temperature of the first AlGaN layer.
According to another aspect of the present invention, a method for driving a light emitting apparatus is provided. The apparatus comprises: a light emitting section for emitting light, a color of the light being blue shifted with a value of a driving current; and a driving section for driving the light emitting section. The method comprises the steps of: receiving a signal designating a desired color and a signal designating a desired intensity; generating the driving current based on the color-designating signal and the intensity-designating signal; and applying the driving current to the light emitting section so that the light emitting section emits light having the desired color and the desired intensity.
In one embodiment of this invention, the method further comprises the steps of: converting the color-designating signal to a signal designating a current value in accordance-with current versus emission wavelength characteristics of the light emitting section; calculating a signal designating a duty based on the intensity-designating signal and the current- value-designating signal, in such a manner that the product of a current value designated by the current value-designating signal and the duty corresponds to the intensity designated by the intensity-designating signal; and generating as the driving current a pulse current having the current value and the duty in accordance with the respective current value-designating signal and duty-designating signal.
In one embodiment of this invention, the light emitting section is an LED device.
In one embodiment of this invention, the light emitting section is an LED bullet comprising an LED device; and a fluorescent excited by light emitted by the LED device to emit light.
In one embodiment of this invention, when the driving current value is changed, a change in an emission wavelength of the LED bullet is larger than a change in an emission wavelength of the LED device.
In one embodiment of this invention, the light emitting apparatus comprises: a plurality of the light emitting sections; and a plurality of the driving sections respectively corresponding to the plurality of the light emitting sections. A color and intensity of light emitted by each of the plurality of the light emitting sections is controlled by a corresponding one of the plurality of the driving sections.
In one embodiment of this Invention, the color-designating signal is a color signal for designating a color of light to be emitted by the LED device, and the intensity-designating signal is an intensity signal for designating an Intensity of the light to be emitted by the LED device.
In one embodiment of this invention, the color-designating signal is a chromaticity signal for designating a color of light to be emitted by the LED bullet, and the intensity-designating signal is a luminance signal for designating an intensity of the light to be emitted by the LED bullet.
In one embodiment of this invention, the LED device comprises: an InGaN active layer; and an AlGaN layer having two layers, provided on the InGaN active layer. One of the two layers is a first AlGaN layer contacting the InGaN active layer, and the other of the two layers of the AlGaN layer is a second AlGaN layer provided on the first AlGaN layer, the first AlGaN layer is produced at substantially the same growth temperature as the InGaN active layer, and the second AlGaN layer is produced at a growth temperature higher than the growth temperature of the first AlGaN layer.
In one embodiment of this invention, the LED device comprises: an InGaN active layer; and an AlGaN layer having two layers, provided on the InGaN active layer. One of the two layers is a first AlGaN layer contacting the InGaN active layer, and the other of the two layers of the AlGaN layer is a second AlGaN layer provided on the first AlGaN layer, the first AlGaN layer is produced at substantially the same growth temperature as the InGaN active layer, and the second AlGaN layer is produced at a growth temperature higher than the growth temperature of the first AlGaN layer.
In one embodiment of this invention, the light emitting section is an LED device, the LED device is driven by a pulse current having a current value and a duty, the current value is set to a value corresponding to an emission wavelength of the LED device, and the duty is set to a value corresponding to an emission intensity of the LED device.
In one embodiment of this invention, the current value is set to a value In a range in which a change In the emission wavelength of the LED device is about 6 nm, and the duty is changed in accordance with the emission intensity of the LED device.
In one embodiment of this invention, the current value is controlled so that the emission wavelength of the LED device is changed, and the duty is controlled so that the emission intensity of the LED device is substantially maintained constant.
In one embodiment of this invention, the light emitting section is an LED bullet comprises: an LED device; and a fluorescent excited by light emitted by the LED device to emit light. An emission wavelength of the LED device is changed by changing the driving current value so that a color of light emitted by the LED bullet is changed.
In one embodiment of this invention, the light emitting section is an LED bullet comprises: an LED device; and a fluorescent excited by light emitted by the LED device to emit light. The LED device is driven by a pulse current having a current value and a duty wherein the current value is set to a value In accordance with current versus emission wavelength characteristics of the LED bullet, and the duty is set to a value in accordance with emission intensity characteristics of the LED bullet.
According to another aspect of the present invention, a display apparatus comprises: a plurality of light emitting sections provided in a plane, light emitted by each of the plurality of light emitting sections being blue shifted with a value of a driving current; and a plurality of driving sections each for driving a corresponding one of the plurality of light emitting sections so that the corresponding one of the plurality of light emitting sections emits light having a desired color and a desired intensity, by each generating the driving current based on a signal designating the desired color and a signal designating the desired intensity and by each applying the driving current to the corresponding one of the plurality of light emitting sections.
In one embodiment of this invention, each of the plurality of light emitting-sections is an LED device.
In one embodiment of this Invention, each of the plurality of light emitting sections is an LED bullet comprising: an LED device; and a fluorescent excited by light emitted by the LED device to emit light.
According to another aspect of the present invention, an LED bullet comprises: an LED device having a light color, the light color being blue shifted with a change in a driving current; and a fluorescent excited by light emitted by the LED device to emit light.
Thus, the invention described herein makes possible the advantages of providing (1) a method for driving an LED device having a light color which is blue shifted with a driving current value, In such a manner that the emission intensity of the LED device is changed while maintaining the light color of the LED device from being changed; (2) a method for driving an LED device in which variation of the emission intensity and light color of the LED device can be suppressed; (3) a method for driving an LED device in which light emitted from the LED device can be changed by utilizing a characteristic of the LED device in which the light color of the LED device is changed with a current driving value; (4) an apparatus for achieving the above-described methods; (5) an LED bullet including an LED device and a fluorescent and capable of providing a wide range of variations in light color; and (6) a method for driving the LED bullet.